JP5702440B2 - Adhesive composition - Google Patents

Description

  The present invention relates to a pressure-sensitive adhesive composition, and more particularly relates to coexistence of wet heat whitening resistance that does not whiten even under wet heat conditions and a low dielectric constant capable of suppressing transmission delay of electronic devices.

  In recent years, in information equipment terminals such as smartphones, device miniaturization has progressed, and high-speed data transmission has been demanded. As part of this, the frequency of electrical signals is increasing, but if high frequency components increase in the electrical signals, the transmission path is likely to be delayed. In order to suppress the transmission delay, it is effective to lower the dielectric constant of the member. Therefore, the adhesive used is required to have a low dielectric constant. In order to reduce the dielectric constant of the pressure-sensitive adhesive, the proportion of the hydrophobic monomer may be increased as a constituent component of the polymer.

On the other hand, in an electronic device, since an adhesive is also used for a visually recognizable part such as a display, transparency is strongly required. Further, it is required not to be whitened even under severe conditions such as high temperature and high humidity. As a method of improving this heat and heat whitening resistance, pressure-sensitive adhesives using various hydrophilic monomers are known. However, since the dielectric constant of the resin tends to increase when hydrophilic monomers are used, It has been difficult to achieve both heat and heat whitening resistance and a low dielectric constant.
Further, when used for assembling a display, if the step of the frame printing portion cannot be filled without a gap, the air layer remains and the appearance is deteriorated, so that the step following ability is also required.

Patent Document 1 discloses a pressure-sensitive adhesive having a low dielectric constant, but it has not been studied for compatibility with moisture and heat whitening performance.
JP 2012-246477

  An object of the present invention is to provide a pressure-sensitive adhesive composition excellent in moisture and heat whitening resistance that does not whiten even under wet heat conditions, a low dielectric constant capable of suppressing transmission delay of electronic equipment, and also excellent in step following ability. .

The present invention is a (meth) acryl having a substituent of either a linear alkyl group having 10 to 24 carbon atoms or a branched alkyl group in a solvent having a solubility in water of 10 g / 100 mL (20 ° C.) or less. An acrylic polymer having a weight average molecular weight of less than 400,000 is obtained by polymerizing a monomer containing 20 to 99% by weight of a monomer and 0.1 to 7% by weight of an amide group-containing monomer. A pressure-sensitive adhesive composition characterized by not containing a solvent having a solubility in water exceeding 10 g / 100 mL (20 ° C.) and having a relative dielectric constant at a frequency of 1 MHz when laminated as a pressure-sensitive adhesive layer It is a thing.

  Since the pressure-sensitive adhesive composition of the present invention is excellent in moisture and heat whitening resistance, transparency can be maintained even when used in an electronic device, and the appearance is excellent. In addition, since the device has a low dielectric constant, the device can be miniaturized and the transmission delay can be suppressed even if the data transmission speed is increased, and it is useful as an adhesive used in information equipment terminals such as smartphones.

  The pressure-sensitive adhesive composition of the present invention comprises 20 to 99% by weight of a (meth) acrylic monomer having a substituent having 10 to 24 carbon atoms, and 0.1 to 7% by weight of an amide group-containing monomer. It contains an acrylic polymer obtained by polymerizing the monomer to be contained and having a weight average molecular weight of less than 400,000.

  As a (meth) acrylic monomer having a substituent having 10 to 24 carbon atoms, a monomer having a linear alkyl group, a monomer having a branched alkyl group, a monomer having a cyclic alkyl group, etc. Is mentioned.

  Monomers having a linear alkyl group include isodecyl (meth) acrylate, undecyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, tetradecyl (meth) acrylate, pentadecyl (meth) acrylate, hexadecyl ( Examples include meth) acrylate, heptadecyl (meth) acrylate, stearyl (meth) acrylate, and behenyl (meth) acrylate.

  Monomers having a branched alkyl group include isodecyl (meth) acrylate, isomistyryl (meth) acrylate, isostearyl (meth) acrylate, propylheptyl (meth) acrylate, isoundecyl (meth) acrylate, isododecyl (meth) acrylate, isotridecyl (Meth) acrylate, isopentadecyl (meth) acrylate, isohexadecyl (meth) acrylate, isoheptadecyl (meth) acrylate, etc. are mentioned.

  Examples of the monomer having a cyclic alkyl group include isobornyl (meth) acrylate, terpene (meth) acrylate, and dicyclopentanyl (meth) acrylate.

  The (meth) acrylic monomer having a substituent having 10 to 24 carbon atoms needs to be used in an amount of 20 to 99% by weight, more preferably 40 to 99% by weight, based on the whole monomer. If it is less than 20% by weight, the resulting adhesive has a high dielectric constant, and if it exceeds 99% by weight, the heat-and-moisture whitening resistance is poor.

Examples of the amide group-containing monomer include acrylamide, methacrylamide, dimethylacrylamide, diethylacrylamide, N-isopropylacrylamide, acryloylmorpholine, N-vinylpyrrolidone, diacetone acrylamide, and the like.
It is necessary to use the amide group-containing monomer in an amount of 0.1 to 7% by weight based on the whole monomer. If it is less than 0.1% by weight, the heat-and-moisture whitening resistance is poor.

  As the monomer constituting the acrylic polymer, other known (meth) acrylic monomers and monomers copolymerizable with (meth) acrylic monomers can be used. Moreover, it is preferable that Tg of acrylic polymer shall be -30 degrees C or less combining these. When the Tg of the acrylic polymer is −30 ° C. or lower, the step following ability can be improved.

  As a (meth) acrylic monomer having a substituent having 9 or less carbon atoms, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, Octyl methacrylate, 2-ethylhexyl methacrylate, isononyl methacrylate.

  Examples of the hydroxyl group-containing (meth) acrylic monomer include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, and methacrylic acid. 3-hydroxypropyl, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, 2-hydroxy-3-chloropropyl acrylate, 2-hydroxy-3-chloropropyl methacrylate, 2-hydroxy-3-phenoxy acrylate And propyl, 2-hydroxy-3-phenoxypropyl methacrylate and the like.

  Examples of (meth) acrylic acid alkoxyesters include 2-methoxyethyl methacrylate, 2-ethoxyethyl methacrylate, 2-methoxypropyl methacrylate, 3-methoxypropyl methacrylate, 2-methoxybutyl methacrylate, 4-methoxy methacrylate. Examples include butyl.

  As (meth) acrylic acid alkylene glycol, ethylene glycol acrylate, polyethylene glycol acrylate, propylene glycol acrylate, polypropylene glycol acrylate, ethylene glycol methacrylate, polyethylene glycol methacrylate, propylene glycol methacrylate, polypropylene glycol methacrylate, etc. Is mentioned.

  Examples of the aryl (meth) acrylate include benzyl acrylate, phenoxyethyl acrylate, phenyl acrylate, benzyl methacrylate, phenoxyethyl methacrylate, and phenyl methacrylate.

  In addition, aromatic vinyl monomers such as styrene, α-methylstyrene, vinyl toluene, ethyl vinyl benzene, saturated fatty acid vinyl monomers such as vinyl acetate, vinyl propionate, vinyl versatate, ethylene, propylene, butadiene Olefinic monomers such as, carboxyl group-containing monomers such as acrylic acid, methacrylic acid and itaconic acid, and polyfunctional monomers such as divinylbenzene, ethylene glycol dimethacrylate and diallyl phthalate.

An acrylic polymer can be synthesized by heating the acrylic monomer together with a polymerization initiator in a solvent, for example. The weight average molecular weight of the acrylic polymer needs to be 400,000 or less, and if it exceeds 400,000, the step following ability deteriorates.
In addition, the weight average molecular weight in this invention means the value measured by GPC (gel permeation chromatography) and calculated by polystyrene conversion. The sample used was a filtrate obtained by dissolving the sample in tetrahydrofuran to make a 0.1 wt% solution, leaving it in an ultrasonic cleaning apparatus to which water was added for 10 minutes, and then filtering through a 0.20 μm membrane filter.
Analyzer: SHIMADZU, LC20AD
Column: GPC-80M x2 made by SHIMADZU
Eluent: Tetrahydrofuran Flow rate: 1.0 ml / min
Inlet pressure: 10kgf
Detector: Differential refractometer (RI)
Column temperature: 40 ° C
Injection volume: 50 μl
Eluent: Tetrahydrofuran Detector: Differential refractometer Standard sample: Polystyrene

  Solvents used for acrylic polymer synthesis include methyl acetate, ethyl acetate, butyl acetate, benzene, toluene, xylene, acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, n-hexane, isopropyl alcohol, n-butanol, propylene glycol monomethyl ether, propylene Examples include organic solvents such as glycol dimethyl ether, propylene glycol monomethyl ether acetate, and propylene carbonate. However, other solvents may be used, and two or more solvents may be used in combination.

The pressure-sensitive adhesive composition of the present invention preferably contains a solvent having a water solubility of 10 g / 100 mL (20 ° C.) or less from the viewpoint of lowering the dielectric constant, and such a solvent was used during the synthesis of the acrylic polymer. In this case, it can be used as an adhesive as it is. In addition, at the time of acrylic polymer synthesis, a solvent having a solubility in water exceeding 10 g / 100 mL (20 ° C.) may be substituted with a solvent having a solubility in water of 10 g / 100 mL (20 ° C.) or less after synthesis. The process becomes complicated.
Examples of the solvent having a solubility in water of 10 g / 100 mL (20 ° C.) or less include ethyl acetate and toluene.

Examples of the polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2,2′-azobis (2,4-dimethyl). Valeronitrile), dimethyl-2,2′-azobis (2-methylpropionate), 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile) 2,2′-azobis [N- (2-propenyl) -2-methoxypropionamide], 1-[(1-cyano-1-methylethyl) azo] formamide, 2,2′-azobis (N-butyl) -2-methylpropionamide), 2,2′-azobis (N-cyclohexyl-2-methylpropionamide), [1,1′-azobis (1-acetoxy-1-phenylethane)], and the like Zo compounds, lauroyl peroxide, octanoyl peroxide, benzoyl peroxide, ethyl methyl ketone peroxide, cumene hydroperoxide, dicumyl peroxide, t-butyl hydroperoxide, cumyl peroxyneodecanoate, t- Hexylperoxyneodecanoate, t-butylperoxy-2-ethylhexanoate, dicumyl peroxide, isobutyl peroxide, di-t-butyl peroxide, t-butylcumyl peroxide, t-butylperoxy Benzoate, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, di (2-ethylhexyl) peroxydicarbonate, 1,1-bis (t-butylperoxy) -3,3 5-trimethylcyclohexa , It can be used 3,3,5 organic peroxide compounds such as trimethyl cyclohexanoyl peroxide and the like.
In addition, the peroxide compound can be subjected to redox polymerization by using a reducing agent such as N, N-dimethyltoluidine, N, N-diethyltoluidine or the like in combination.
The polymerization initiator is usually used in an amount of 0.05 to 3 parts by weight based on 100 parts by weight of the acrylic monomer. Increasing the amount of polymerization initiator used tends to decrease the molecular weight of the polymer obtained, and decreasing the amount of polymerization initiator used tends to increase the molecular weight of the polymer obtained.

The pressure-sensitive adhesive composition of the present invention preferably has a relative dielectric constant of 3 or less at a frequency of 1 MHz. As a method for measuring the relative dielectric constant, a pressure-sensitive adhesive layer (a film obtained by peeling a PET film subjected to silicone treatment from a pressure-sensitive adhesive sheet) is laminated to form a laminated pressure-sensitive adhesive layer of about 200 μm. The relative dielectric constant was measured by the following apparatus. In the measurement, the average of the measured values of the three samples was taken as the dielectric constant.
Measurement method: LCR meter (Device: Wayne Kerr 6440B using impedance analyzer)
Frequency: 1MHz
Bias voltage: 2V
Measurement environment: 23 ± 1 ℃, 50 ± 1% RH

  A crosslinking agent can be further added to the pressure-sensitive adhesive composition of the present invention. Examples of the crosslinking agent include isocyanate compounds and epoxy compounds. Isocyanate compounds include aromatic isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, naphthalene diisocyanate, and p-phenylene diisocyanate, and aliphatic isocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, nobornene diisocyanate, and dicyclohexylmethane diisocyanate. And hydrogenated products of the above aromatic diisocyanates such as isophorone diisocyanate and hydrogenated xylene diisocyanate. Also, reaction products of polyfunctionalized polyisocyanate structures such as adduct type, isocyanurate type, biuret type, polymethylene polyphenyl polyisocyanate, polyester polyisocyanate, polyether polyisocyanate, trimethylolpropane modified polyisocyanate, etc. It may be a thing.

  Examples of the epoxy compound include ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, bisphenol A / epichlorohydrin type epoxy resin, N, N, N′N′-tetraglycidyl- Examples thereof include m-xylenediamine, 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N-diglycidylaniline, N, N-diglycidyltoluidine and the like.

  In addition, a metal complex compound may be added. Examples of the metal complex compound include compounds in which acetylacetone, ethyl acetoacetate, and the like are coordinated to a polyvalent metal such as aluminum, iron, copper, zinc, tin, titanium, nickel, antimony, magnesium, vanadium, chromium, and zirconium. . Specific examples include nursem aluminum (trade name, manufactured by Nippon Chemical Industry Co., Ltd.) in which acetylacetone is coordinated to aluminum.

  Various additions such as ultraviolet absorbers, near infrared absorbers, antioxidants, antiseptics, antifungal agents, tackifier resins, plasticizers, antifoaming agents, and wettability adjusting agents are added to the adhesive composition of the present invention. An agent may be included.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and demonstrated in detail about this invention, a specific example is shown and it does not specifically limit to these.

Example 1
In a separable flask equipped with a stirrer and a reflux condenser, 95 parts by weight of n-decyl methacrylate (DMA), 4 parts by weight of acrylamide (AAm) and 1 part by weight of 4-hydroxybutyl acrylate (4HBA) as monomers, polymerization started 0.23 parts of azobisisobutyronitrile as an agent and 77 parts of ethyl acetate as a solvent were added, and nitrogen gas was introduced for 30 minutes or more to remove oxygen in the polymerization system. The temperature was raised to 75 ° C. at a rate of 1 ° C./1 min, stirred for 4 hours while maintaining 75 ± 1 ° C., 0.06 part of azobisvaleronitrile was added, the reaction temperature was raised to 80 ° C., and 80 hours 2 hours. Aging was performed while maintaining ± 1 ° C. After completion of the reaction, the reaction solution was diluted with ethyl acetate to obtain a polymer solution of Example 1 which was a pale yellow transparent viscous liquid. The viscosity was 4000 mPa · s, the solid content was 50%, and the weight average molecular weight was 240,000.

  To 100 parts by weight of the solid content of the polymer solution of Example 1, 1.5 parts by weight of coronate HX (trade name, manufactured by Nippon Polyurethane Industry Co., Ltd.), which is a polyfunctional isocyanate compound, is added as a crosslinking agent, and further 23 parts by weight of ethyl acetate. To prepare a pressure-sensitive adhesive composition of Example 1 to a solid content of 45%.

Examples 2-9, Comparative Examples 1-4
In addition to the materials used in Example 1, monomers include IDMA (iso-decyl methacrylate), LMA (lauryl methacrylate), STMA (stearyl methacrylate), ISTA (iso-stearyl acrylate), NVP (N-vinylpyrrolidone), DAAM (diacetone acrylamide), DMAAm (dimethyl acrylamide), BA (butyl acrylate), 2EHA (2-ethylhexyl acrylate), toluene, MEK (methyl ethyl ketone) as a solvent, and a coronate which is a polyfunctional isocyanate compound as a crosslinking agent L, Coronate HL (both manufactured by Nippon Polyurethane Industry Co., Ltd., both trade names) were used in the same manner as in Example 1 except that the polymer was polymerized and blended according to the formulation shown in Table 1, and the solid content was 45%. Examples 2-9, Comparative Examples 1 Each adhesive composition was prepared.

Preparation of pressure-sensitive adhesive sheet Each pressure-sensitive adhesive composition was applied onto a release film so that the thickness after drying was 100 μm, dried by heating at 90 ° C. for 20 minutes, and then a release film (silicone-treated PET film). And aged at 23 ° C. for 7 days to prepare a base material-less pressure-sensitive adhesive sheet.

Moisture and heat whitening-resistant pressure-sensitive adhesive sheets were bonded to a PET film (trade name A4300, manufactured by Toyobo Co., Ltd., thickness 50 μm) to form a film piece having a width of 25 mm and a length of 100 mm. The release film of the film piece was peeled off and stuck on glass at 23 ° C. and 50% RH atmosphere using a laminator. This was allowed to stand for 400 hours in an environment of 60 ° C. and 95% RH, and the haze after cooling at 23 ° C. and 50% RH for 1 hour was measured. In addition, haze was measured using Toyo Seiki Seisakusho Co., Ltd. HAZE-GARDII. The evaluation criteria are as follows.
◯: Haze is less than 1.5 (almost no whitening is confirmed and moisture and heat whitening resistance is good)
X: Haze is 1.5 or more (cannot be used due to poor whitening property)

It printed on the level | step difference followable PET film so that a level | step difference might be set to 40 micrometers by 1 cm in width | variety with a silk screen coater using silver ink. The release liner of the pressure-sensitive adhesive tape for test was peeled off at 23 ° C. and 50% RH, and pasted using a laminator so as to straddle the printing surface of the printing film (size 40 mm × length 100 mm). This was treated in an autoclave at 50 ° C. and 0.5 MPa for 20 minutes, and then allowed to stand in an environment of 23 ° C. and 50% RH for 24 hours. If the step was buried after laminator attachment and immediately after the autoclave treatment, the step followability was good (◯), and if the step was not filled immediately after the autoclave treatment, the step followability was poor (x).

  Each of the pressure-sensitive adhesive compositions of Examples had a low dielectric constant, and also had good resistance to moist heat whitening and step following ability. On the other hand, in each adhesive composition of the comparative example, the dielectric constant was high, and the resistance to moist heat whitening and the step following ability were not sufficient.

Claims (4)

(Meth) acrylic monomer having a substituent of either a linear alkyl group having 10 to 24 carbon atoms or a branched alkyl group in a solvent having a solubility in water of 10 g / 100 mL (20 ° C.) or less Containing an acrylic polymer having a weight average molecular weight of less than 400,000, obtained by polymerizing a monomer containing 20 to 99% by weight of a body and 0.1 to 7% by weight of an amide group-containing monomer, A pressure-sensitive adhesive composition characterized by not containing a solvent whose solubility in water exceeds 10 g / 100 mL (20 ° C.) and having a relative dielectric constant at a frequency of 1 MHz when laminated as a pressure-sensitive adhesive layer . The pressure-sensitive adhesive composition of claim 1 wherein the Tg of the acrylic polymer is -30 ° C. or less.   The pressure-sensitive adhesive composition according to claim 1 or 2, wherein the acrylic polymer is obtained by polymerizing a monomer containing a hydroxyl group-containing (meth) acrylic monomer. The pressure-sensitive adhesive composition according to claim 1 , wherein the amide group-containing monomer does not have a cyclic structure.